Check if the port-channel is up or not: "show interfaces port-Channel <id>"

If the port-channel is up, make sure all Vlan is present on the port-channel: "show vlan"

If the concerned Vlan is present, check the Spanning-tree status: show spanning-tree

If it is RPVST, check if the port-channel is in "forwarding state" in all the concerned Vlans

If it is MSTP, check if the port-channel is in "forwarding-state" in the instance which includes your concerned Vlans.

Also check the Spanning-tree status on Juniper side as well.

It might be possible that the Arista switch is forwarding the traffic out of the port-channel and getting dropped on the other side. You can confirm if Arista is forwarding the traffic or not using Outbound ACL Counters on the port-channel. See the below example:

Consider the port-channel is Po9 and the source-IP is 1.1.1.1 and destination IP is 2.2.2.2. Create the ACL as below:

^ As you can see in this case, the counter for the flow (Source-1.1.1.1, destination-2.2.2.2) is incrementing which proves packets are getting forwarded out of port-channel9. If it doesn't increment, then it means it is getting dropped on Arista for some reason (which we need to check).

Note: The IP ACL test is useless if ARP is not resolved on Source host (either for it's GW or of another host in same Vlan it is trying to ping). In that case, make sure to configure a static ARP on the source host. If static ARP cannot be programmed, then instead of IP ACL test, we need to do MAC ACL test. Let us know if you need help with that. Also ensure Source host is actually sending traffic.

Just wanted to let you know, Arista has the following platforms where you can capture packets that are switched/routed in Hardware by mirroring them to CPU, like: 7280R Series, 7500R series, 7020R series, 7160 series and 7150 series

7050 and 7060 series didn't have the mirroring to CPU support for quite some time. But now since the release of EOS-4.24.0F version (and later versions), even these two series (along with few others which didn't have the support before) supports packet mirroring to CPU.
Please see the following TOI: Mirror to CPU on 7060 & 7050

Using the feature- "Mirroring to CPU" you can mirror any packet, that is getting switched or routed in the Hardware, to the CPU and capture those packets in the CPU itself. Generally packets that are switched/routed in Hardware will not go to the CPU. It is a great tool for troubleshooting and inspection of packets in the network.

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